Spectrometry-based gas analyzers, such as Fourier transform infrared spectrometry (FTIR) gas analyzers, are becoming common for environmental compliance applications and process gas monitoring, in addition to other gas analysis applications. They are generally good for measuring compounds from 0.1 parts per million (ppm) to a few percent levels in an environmental exhaust, for example. On the other hand, spectrometry-based gas analyzers generally perform poorly when parts per billion (ppb) detection levels are required. Moreover, if too many compounds are present (e.g., greater than 10-20) or too many unknowns are present, the analysis of the spectral data becomes too difficult and the results somewhat questionable.
Gas chromatography (GC) is an analytical method that measures the content of various components in a sample. The method for separating chemical substances relies on differences in partitioning behavior between a flowing mobile phase (gas phase) and a stationary phase supported in a column to separate the components in a mixture. As the gas flow passes through the column, the components of the sample move at velocities that are influenced by the degree of interaction of each component with the stationary phase in the column. Consequently, the different components separate as the components elute from the column.
Gas chromatography can be utilized for many compounds but also has many drawbacks, which include a need for full peak separation to qualify and quantify compounds present, small sample sizes and dynamic ranges, and continuing calibration.
Combined GC-FTIR systems are also known in the industry but are not widely accepted because other GC detectors are more sensitive.